Based on earlier work on the construction of the diadem, the name-giving feature of the genus Trichodiadema, the results of fresh investigations with a focus on plants that lack “true diadems” are presented. The possession of stiff prickly bristles can be understood to form the probable synapomorphy of all members of the genus, the main chemical component being suberin. More extensive studies of flowers and capsules permit a subdivision of the genus into two subgenera, and T. subg. Gemiclausa is described here as a new subgenus. A key to the six included species is given, and all species of the new subgenus are described.